The probiotic properties of different preparations using Lactococcus lactis Z-2 on intestinal tract, blood and hepatopancreas in Cyprinus carpio

Abstract Basing on the beneficial effects of live Lactococcus lactis Z-2 and its extracellular polysaccharides on the common carp (Cyprinus carpio L.) in the previous studies, the present study aims may be appropriate to investigate the functions of other forms of L. lactis Z-2 (namely, heat-killed or cellular components) on the intestinal tract, blood and hepatopancreas of common carp. 480 fish [(42.35 ± 0.76) g] were treated with different preparations of L. lactis Z-2 for 7 days and infected with Aeromonas hydrophila for 24 h, following which to detect the levels of NO and cytokines, the activities of lysozyme (LZM) and alkaline phosphatase (AKP) in the serum, the antioxidants (T-AOC, SOD, CAT, GSH, GSH-Px and MDA) in hepatopancreas, the digestive enzymes and the gene expression of nutrient transporters in intestinal. Prior to infection, different treatment groups significantly enhanced NO production, the levels of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6), AKP activity, antioxidant content (T-AOC, SOD, CAT, and GSH), and reduced MDA level compared to those in the negative control group (P